1. Field of Inventions
The present inventions relate generally to surgical probes that support therapeutic devices in contact with body tissue.
2. Description of the Related Art
There are many instances where diagnostic and therapeutic elements must be inserted into the body. One instance involves the treatment of cardiac conditions such as atrial fibrillation and atrial flutter which lead to an unpleasant, irregular heart beat, called arrhythmia.
Normal sinus rhythm of the heart begins with the sinoatrial node (or “SA node”) generating an electrical impulse. The impulse usually propagates uniformly across the right and left atria and the atrial septum to the atrioventricular node (or “AV node”). This propagation causes the atria to contract in an organized way to transport blood from the atria to the ventricles, and to provide timed stimulation of the ventricles. The AV node regulates the propagation delay to the atrioventricular bundle (or “HIS” bundle). This coordination of the electrical activity of the heart causes atrial systole during ventricular diastole. This, in turn, improves the mechanical function of the heart. Atrial fibrillation occurs when anatomical obstacles in the heart disrupt the normally uniform propagation of electrical impulses in the atria. These anatomical obstacles (called “conduction blocks”) can cause the electrical impulse to degenerate into several circular wavelets that circulate about the obstacles. These wavelets, called “reentry circuits,” disrupt the normally uniform activation of the left and right atria.
Because of a loss of atrioventricular synchrony, the people who suffer from atrial fibrillation and flutter also suffer the consequences of impaired hemodynamics and loss of cardiac efficiency. They are also at greater risk of stroke and other thromboembolic complications because of loss of effective contraction and atrial stasis.
One surgical method of treating atrial fibrillation by interrupting pathways for reentry circuits is the so-called “maze procedure” which relies on a prescribed pattern of incisions to anatomically create a convoluted path, or maze, for electrical propagation within the left and right atria. The incisions direct the electrical impulse from the SA node along a specified route through all regions of both atria, causing uniform contraction required for normal atrial transport function. The incisions finally direct the impulse to the AV node to activate the ventricles, restoring normal atrioventricular synchrony. The incisions are also carefully placed to interrupt the conduction routes of the most common reentry circuits. The maze procedure has been found very effective in curing atrial fibrillation. However, the maze procedure is technically difficult to do.
Maze-like procedures have also been developed utilizing catheters which can form lesions on the endocardium (the lesions being 1 to 15 cm in length and of varying shape) to effectively create a maze for electrical conduction in a predetermined path. The formation of these lesions by soft tissue coagulation (also referred to as “ablation”) can provide the same therapeutic benefits that the complex incision patterns that the surgical maze procedure presently provides.
Catheters used to create lesions typically include a relatively long and relatively flexible body portion that has a soft tissue coagulation electrode on its distal end and/or a series of spaced tissue coagulation electrodes near the distal end. The proximal end of the flexible body is typically connected to a handle which includes steering controls. The portion of the catheter body portion that is inserted into the patient is typically from 58.4 cm to 139.7 cm in length and there may be another 20.3 cm to 38.1 cm, including a handle, outside the patient. The length and flexibility of the catheter body allow the catheter to be inserted into a main vein or artery (typically the femoral artery), directed into the interior of the heart, and then manipulated such that the coagulation electrode contacts the tissue that is to be ablated. Linear and curvilinear lesions can then be created by dragging a single electrode or by applying power (preferably simultaneously) to the series of spaced electrodes.
Catheter-based soft tissue coagulation has proven to be a significant advance in the medical arts generally and in the treatment of cardiac conditions in particular. Nevertheless, the inventors herein have determined that catheter-based procedures are not appropriate in every situation and that conventional catheters are not capable of reliably forming all types of lesions. For example, one lesion that has proven to be difficult to form with conventional catheter devices is the circumferential lesion that is used to isolate the pulmonary vein and cure ectopic atrial fibrillation. Lesions that isolate the pulmonary vein may be formed within the pulmonary vein itself or in the tissue surrounding the pulmonary vein. These circumferential lesions are formed by dragging a tip electrode around the pulmonary vein or by creating a group of interconnected curvilinear lesions one-by-one around the pulmonary vein. Such techniques have proven to be less than effective because they are slow and gaps of conductive tissue can remain after the procedure. It can also be difficult to achieve the adequate tissue contact with conventional catheters.
Accordingly, the inventors herein have determined that a need exists for structures that can be used to create circumferential lesions within or around bodily orifices and, in the context of the treatment of atrial fibrillation, within or around the pulmonary vein.
Another instance where therapeutic elements are inserted into the body is the treatment of tumors, such as the cancerous tumors associated with breast cancer and liver cancer. Heretofore, tumors have been treated with highly toxic drugs that have proven to have severe side effects. More recently, devices including a plurality of needle-like electrodes have been introduced. The needle-like electrodes may be directed into the tumor tissue and used to deliver RF energy. The associated current flow heats the tissue and causes it to coagulate.
The inventors herein have determined that there are a number of shortcomings associated with the use of needle-like electrodes to coagulate tissue. Most notably, the needle-like electrodes produce non-uniform, shallow lesions and/or spot lesions and also fail to coagulate the entire volume of tumor tissue. This failure can ultimately result in the tumor growing to be even larger than its original size. The needle-like electrodes can also cause tissue charring. Moreover, tissue tends to shrink around the needle-like electrodes during the coagulation process. This makes it very difficult to withdraw the electrodes from the patient and often results in tissue trauma.
Accordingly, the inventors herein have determined that a need exists for a device that can completely and uniformly coagulate large volumes of tissue without charring and can also be removed from the patient without the difficulty associated with needle-like electrodes.